1. Field of the Invention
This invention relates broadly to the art of physical fitness exercisers and, more specifically, to the field of energy converting exercise mechanisms which provide means whereby the user can exercise selected muscle groups by overcoming resistance in repeated strokes or operational cycles of movement of one portion of the device relative to another portion.
2. Description of the Prior Art
Exercise devices of many types have been developed to allow the user to push or pull some portion of the device to the extent necessary to overcome resistance provided by the mechanism and thereby to allow the user to do work beneficial to particular muscles as an exercise for improving muscle tone and strength. One well-known category of such devices is characterized by the extension or compression of a yielding element such as a spring or rubber cord. A major disadvantage of such devices lies in the fact that the resistance provided is non-uniform, that is, the force required to overcome resistance through a working stroke varies from very little at the outset of deflection of the yielding member to some maximum level the user is able or willing to exert at an extended or compressed, as the case may be, state of deflection of the yielding member. Thus, the muscles involved do little or no effective work during the early portion of a stroke, on the one hand, and may be seriously over-stressed at the limit of deflection achieved by an over-zealous person. A further disadvantage of spring or elastic member exercise devices is the fact that resistance can usually be provided in but one sense of movement of one portion of the device relative to another, so that in any given exercise only those muscles overcoming that uni-directional resistance can be exercised. It is clearly more efficient and beneficial to exercise two synergistic sets of muscles in a given exercise routine as is possible with devices providing bi-directional resistance.
Another group of prior art exercise devices employs, for yielding resistance to be overcome by the user, various frictional means for converting the power output of the user into heat as he moves one portion of the device relative to another. Within this group are devices in which a flexible rope or cord is drawn by the user through a frictionally resistant tortuous path of movement among mechanical elements in a housing, or the rope or cord is squeezed by a braking device within a housing so that drawing the rope or cord through the housing is rendered difficult to a degree established by the user to the best of his ability. Among the disadvantages of this type of device is the great difficulty with which a desired level of resistance can be established by the user for any given exercise since the degree of frictional resistance to an applied force to draw the rope or cord through the device is heavily influenced by factors not controllable at all or controlled poorly at best by the user. A major and poorly controlled factor is the amount of back-tension in that portion of the rope or cord entering the resistance generating housing as the rope or cord is drawn through. Moderate back-tension can result in virtual immobilization of the unit thus defeating its purpose. Varying stiffness and thickness of the rope or cord can likewise produce highly variable resistance to the desired movement.
A further type of frictionally resistant mechanism which has been employed in exerciser devices involves a rigid shaft and a housing surrounding the shaft, such housing being fitted with braking means circumferentially engaging the shaft so that relative axial movement of shaft and housing may be variably resisted by the braking means. One such device incorporates in the housing a rope or cord wrapped around the shaft a number of turns. By varying the tension in this rope or cord, radial pressure of the rope or cord against the shaft is varied to provide a desired degree of frictional engagement of cord and shaft and thereby a desired level of resistance to movement of the shaft relative to the housing. Another device of this general type involves a number of circumferential rings of elastomeric material surrounding the shaft and enclosed in a housing. By compressing the stack of rings to varying degree in a confined zone by means of a threaded end cap on the housing, the rings are caused to grip the shaft through the medium of a sleeve-like member interposed between the shaft and the rings. Thus, a braking effect can be controlled to some extent. Both the aforementioned devices have the disadvantage of being highly sensitive to slight variations in diameter of the shaft along its working length. Thus, major variations in resistance to axial movement of the shaft relative to the circumferential braking means may be exhibited unless the shaft is a highly refined and consequently costly member.
Prior art devices discussed above exhibit a further common disadvantage, namely, that the user is provided no way of determining quantitatively what degree of resistance he is overcoming and therefore what force he is applying as he drives the moving element with respect to the fixed portion of the device. Accurate information on applied force is essential to performance of optimally designed exercise routines.